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54 S E C T I O N 8 Two different statistical models were used in this research to quantify the transportation- related GHG emissions and energy use related to land use changes that can be attributed to transit. Each model used a separate, detailed dataset and provided new evidence of the land use effect. As with any research based on statistical analysis, this research is limited by the data that could be collected and analyzed. Some topics that stand out as areas for further data collection and research are discussed below. Different approaches to measuring density should be explored. The urbanized area model used gross regional population density as the measure of urban form, in part because that data point is readily available for multiple urbanized areas. Using gross density in statistical models could understate the magnitude of the land use effect. Population-weighted densities are a better way to represent the variation in densities across large urban areas. Calculation of population- weighted densities would require a substantial data collection and processing effort, but the potential gains for the statistical modeling are large. Land use planning factors need to be considered in a way that can better inform transit planning processes. Transit agencies are interested in using information on the land use benefits of transit to plan or prioritize transit investments in terms of specific transit modes, routes, and station locations. The amount of development that could be expected within specific timeframes, in response to specific investments, is of particular interest. In order to increase the utility of the land use research for planning purposes, more information is needed on the influence of real estate market factors and public support for compact development on rates of development. These factors have a substantial but unquantified effect on development patterns. Data collection on these topics is a challenge for several reasons. First, tracking detailed development patterns requires the use of parcel-level land data, which are complicated to collect and must be gathered region by region. Second, tracking trends over time requires gathering data for multiple different years. Third, real estate markets and political environments are highly complex and resist being categorized in ways that are discrete and measurable. An innovative approach to considering these factors in terms of the land use effect is needed. Future work could incorporate more research on predicting the market development potential of particular corridors or neighborhoods or further develop the typologies of market strength and public support used in the ITDP study. Future research may also rely on more qualitative analy- sis, âLEED-style,â point-based rating systems, or ranges of uncertainty in prediction. In terms of quantifiable land use benefits, transit agencies could claim some credit for land use plans that they help to develop. Research on this topic would benefit from collaboration with land use planning agencies and the real estate industry. Future Research
Future Research 55 The relationship of transit vehicle capacity to land use development should be explored further. There is an obvious relationship between land use densities and transit vehicle capaci- ties, with higher capacity vehicles generally used in denser areas. While using higher capacity vehicles probably would not encourage densification in and of itself, transit agencies would ben- efit from more information about the relationships between vehicle capacity and land use pat- terns. Such a study could include case research on methods that transit agencies use to determine appropriate transit vehicle capacities or instances where development around transit coincided with an increase in transit vehicle capacities.
